Sources disagree on the reconstruction of this word. Some reconstruct it with initial *h₃- because of Greek ὄνομα ‎(ónoma), ὄνυμα ‎(ónuma), but the lack of an initial laryngeal in Hittite 𒆷𒀀𒈠𒀭 ‎(lāman) suggests *h₁, and Armenian անուն ‎(anun) could be from either one. The Greek o- would then be due to assimilation to the following o-, just as in ὀδούς ‎(odoús, “tooth”), from *odonts, assimilated from *edonts, from *h₁dont-. Medial *-eh₃- is sometimes reconstructed on the basis of length in some Dutch and Low German denominal verbs (in Indo-Iranian it arose by Brugmann's law, and in Latin by analogy cōg-nōmen ‎(“surname”) : co-gnōscō ‎(“to know”), from PIE *ǵneh₃), but these are more likely to be late forms using the Germanic a/ō ablaut found also in class VI strong verbs.

Cowgill and Beekes (1969) have argued that initial e-/o- of Greek and inital a- of Armenian are simply prothetic vowels, i.e. not of laryngeal origin, which would then render the reconstruction as *nómn̥.

The original paradigm is also somewhat difficult to reconstruct precisely; it might be proterokinetic ablauting *h₁nómn̥ ~ *h₁n̥méns, or just acrostatic with or without zero grade in weak cases. The Tocharian forms seem to come from *(h₁)nem-, which could be from the oblique form in an acrostatic paradigm.

In any case, there are lots of puzzles in this word, even though it has reflexes in (almost) all the daughter branches.